DIGESTIVE SYSTEM DIGESTIVE SYSTEM Objectives: - Identify the organs of the digestive system and list their major functions. (stomach, small intestine, large intestine and salivary glands, pancreas, liver, gall bladder) - Explain the processes by which materials move through the digestive tract. - Outline the mechanisms that regulate digestion. The digestive system consists of a muscular tube, the digestive tract, also called the gastrointestinal tract (GI) or alimentary canal, and various accessory organs. The nutrition for the cells of the body must be in a simple The nutrition for the cells of the body must be in a simple form: amino acids, simple sugars, and fatty acids. form: amino acids, simple sugars, and fatty acids. The digestion process: The digestion process: The digestive system takes the The digestive system takes the complex organic molecules of the foods we ingest — complex organic molecules of the foods we ingest — proteins, carbohydrates, and fats — and break them down proteins, carbohydrates, and fats — and break them down into their simple form. The simple molecules (nutrients) are into their simple form. The simple molecules (nutrients) are absorbed from the digestive system by the cardiovascular absorbed from the digestive system by the cardiovascular and lymphatic systems and transported to cells throughout and lymphatic systems and transported to cells throughout the body. the body. The digestive system may The digestive system may divide into two parts: divide into two parts: - A muscular tube, known - A muscular tube, known as the alimentary canal or as the alimentary canal or digestive tract: the mouth, digestive tract: the mouth, pharynx, esophagus, pharynx, esophagus, stomach, small intestine, and stomach, small intestine, and large intestine. large intestine. - The accessory digestive - The accessory digestive organs and glands that help organs and glands that help in the digestive process in the digestive process include the tongue, teeth, include the tongue, teeth, salivary glands, pancreas, salivary glands, pancreas, liver, and gall bladder. liver, and gall bladder. Functions of the Digestive System : - Ingestion occurs when materials enter the digestive tract via the mouth. Ingestion is an active process involving conscious choice and decision making. - Mechanical processing is crushing and shearing that makes materials easier to propel along the digestive tract. It also increases their surface area, making them more susceptible to enzymatic attack. - Digestion refers to the chemical breakdown of food into small organic fragments suitable for absorption by the digestive epithelium. Simple molecules in food, such as glucose, can be absorbed intact, but epithelial cells cannot to absorb molecules the size and complexity of proteins, polysaccharides, or triglycerides. These molecules must be splitted by digestive enzymes prior to absorption. - Secretion is the release of water, acids, enzymes, buffers, and salts by the epithelium of the digestive tract and by glandular organs. - Absorption is the movement of organic substrates, electrolytes (inorganic ions), vitamins, and water across the digestive epithelium and into the interstitial fluid of the digestive tract. - Excretion is the removal of waste products from body fluids. Peristalsis : - The muscularis externa propels materials from one portion of the Digestive System Regulation Digestive System Regulation Bởi: OpenStaxCollege The brain is the control center for the sensation of hunger and satiety The functions of the digestive system are regulated through neural and hormonal responses Neural Responses to Food In reaction to the smell, sight, or thought of food, like that shown in [link], the first hormonal response is that of salivation The salivary glands secrete more saliva in response to the stimulus presented by food in preparation for digestion Simultaneously, the stomach begins to produce hydrochloric acid to digest the food Recall that the peristaltic movements of the esophagus and other organs of the digestive tract are under the control of the brain The brain prepares these muscles for movement as well When the stomach is full, the part of the brain that detects satiety signals fullness There are three overlapping phases of gastric control—the cephalic phase, the gastric phase, and the intestinal phase—each requires many enzymes and is under neural control as well Seeing a plate of food triggers the secretion of saliva in the mouth and the production of HCL in the stomach (credit: Kelly Bailey) 1/4 Digestive System Regulation Digestive Phases The response to food begins even before food enters the mouth The first phase of ingestion, called the cephalic phase, is controlled by the neural response to the stimulus provided by food All aspects—such as sight, sense, and smell—trigger the neural responses resulting in salivation and secretion of gastric juices The gastric and salivary secretion in the cephalic phase can also take place due to the thought of food Right now, if you think about a piece of chocolate or a crispy potato chip, the increase in salivation is a cephalic phase response to the thought The central nervous system prepares the stomach to receive food The gastric phase begins once the food arrives in the stomach It builds on the stimulation provided during the cephalic phase Gastric acids and enzymes process the ingested materials The gastric phase is stimulated by (1) distension of the stomach, (2) a decrease in the pH of the gastric contents, and (3) the presence of undigested material This phase consists of local, hormonal, and neural responses These responses stimulate secretions and powerful contractions The intestinal phase begins when chyme enters the small intestine triggering digestive secretions This phase controls the rate of gastric emptying In addition to gastrin emptying, when chyme enters the small intestine, it triggers other hormonal and neural events that coordinate the activities of the intestinal tract, pancreas, liver, and gallbladder Hormonal Responses to Food The endocrine system controls the response of the various glands in the body and the release of hormones at the appropriate times One of the important factors under hormonal control is the stomach acid environment During the gastric phase, the hormone gastrin is secreted by G cells in the stomach in response to the presence of proteins Gastrin stimulates the release of stomach acid, or hydrochloric acid (HCl) which aids in the digestion of the proteins However, when the stomach is emptied, the acidic environment need not be maintained and a hormone called somatostatin stops the release of hydrochloric acid This is controlled by a negative feedback mechanism In the duodenum, digestive secretions from the liver, pancreas, and gallbladder play an important role in digesting chyme during the intestinal phase In order to neutralize the acidic chyme, a hormone called secretin stimulates the pancreas to produce alkaline bicarbonate solution and deliver it to the duodenum Secretin acts in tandem with another hormone called cholecystokinin (CCK) Not only does CCK stimulate the 2/4 Digestive System Regulation pancreas to produce the requisite pancreatic juices, it also stimulates the gallbladder to release bile into the duodenum Link to Learning Visit this website to learn more about the endocrine system Review the text and watch the animation of how control is implemented in the endocrine system Another level of hormonal control occurs in response to the composition of food Foods high in lipids take a long time to digest A hormone called gastric inhibitory peptide is secreted by the small intestine to slow down the peristaltic movements of the intestine to allow fatty foods more time to be digested and absorbed Understanding the hormonal control of the digestive system is an important area of ongoing research Scientists are exploring the role of each hormone in the digestive process and developing ways to target these hormones Advances could lead to knowledge that may help to battle the obesity epidemic Section Summary The brain and the endocrine system control digestive processes The brain controls the responses of hunger and satiety The endocrine system controls the release of hormones and enzymes required for digestion of food in the digestive tract Review ...Introduction Immunity against pathogens and cancer requires cell-cell interactions, the type, strength, and duration of which determine to a large extent the fi nal outcome of the immune response. In this process, T cells transiently interact with specialised antigen presenting cells (APCs) to sample the nature of the prevalent antigens in the body. Recognition of foreign antigen by the T cell receptor (TCR) results in the strengthening of the Tcell- APC interaction, which is primarily mediated by an increase in the affi nity of integrins for their corresponding ligand in a process known as ‘inside-out signalling’ [1]. e resulting stable interaction between a T cell and its cognate APC is the formation of a synapse between the two cells, generally referred to as the immunological synapse (IS) [2] owing to its similarity to the neuronal synapse [3]. e strength and duration of cell-cell interactions play a critical role in the activation of T cells; thus, a reduced capability to interact might result in failure to generate a good response when needed, where- as increased and/or sustained interaction might result in a breach of tolerance against self antigens, leading to the development of autoimmunity. e formation of a mature IS has been characterized recently using advances in imaging techniques [4]. Initial activation of the TCR leads to the rapid formation of microclusters that contain phosphorylated-active TCR associated with the proximal signalling proteins Lck, ZAP-70 and LAT [5,6]. ese microclusters are active signalling structures involving the actin cytoskeleton, since inhibition of actin polymerization prevents their formation [7]. e TCR microclusters coalesce to form the central region of the IS - known as the central supramolecular activation cluster (cSMAC) - which also contains important coreceptors, such as CD4 and CD28, and key signalling proteins, such as PKCθ [7-9]. Recep- tors accommodated in the cSMAC are of small molecular mass, while large and heavily glycosylated proteins, such as LFA-1 (lymphocyte function-associated antigen 1), CD43, and the tyrosine phosphatase CD45, accumulate in a ring around the central region called the peripheral supramolecular activation cluster (pSMAC) [10,11]. e mature IS with its defi ned areas is thought to control various cell-cell interaction-mediated processes by infl uencing signal transduction, leading to diff erential cell functions, and also signal termination and dissolution of cell conjugates [12,13]. Interestingly, recent studies have shown that certain proteins with an established function in the neuronal synapse are also expressed by diff erent T cell subsets. For example, regulatory T cells (Tregs), which are shown to be better poised to interact with APCs compared to naïve T helper ( ) cells, express neuropilin-1 [14]. is molecule enhanced Treg interaction with APCs and its down-regulation by means of small interfering RNA resulted in a concomitant reduction in the ability of Tregs to form long-lasting synapses. Neuropilin-1 was not detected in naïve cells and this lack of expression correlated with their reduced capacity to form stable synapses. Interestingly, ectopic expression of neuropilin-1 Abstract Agrin plays a crucial role in the maintenance of the neuromuscular junction. However, it is expressed in other tissues as well, including T lymphocytes, where cell activation induces its expression. Agrin from activated T cells has the capacity to induce aggregation of key receptors and to regulate signalling. Interestingly, T cells isolated from patients with systemic lupus erythematosus over-express Agrin and its co-stimulation with the T cell receptor enhances production of pathogenic cytokines. These early studies point to an important function for Agrin in Tcell biology and make the case for a more thorough and systematic investigation into its role in the immune system. © 2010 Digestive System Digestion • Phases Include Ingestion Movement Mechanical and Chemical Digestion Absorption Elimination Digestion • Types – Mechanical (physical) • Chew • Tear • Grind • Mash • Mix – Chemical • Enzymatic reactions to improve digestion of – Carbohydrates – Proteins – Lipids Digestive System Organization • Gastrointestinal (Gl) tract – – – Tube within a tube Direct link/path between organs Structures • • • • • • • Mouth Pharynx Esophagus Stomach Small intestine Large Intestine Rectum Mouth • Teeth mechanically break down food into small pieces Tongue mixes food with saliva (contains amylase, which helps break down starch) • Epiglottis is a flap-like structure at the back of the throat that closes over the trachea preventing food from entering it It is located in the Pharynx Esophagus • Approximately 20 cm long • Functions include: Secrete mucus Moves food from the throat to the stomach using muscle movement called peristalsis • If acid from the stomach gets in here that’s heartburn Mouth, Pharynx and Esophagus Video Stomach • J-shaped muscular bag that stores the food you eat, breaks it down into tiny pieces • Mixes food with Digestive Juices that contain enzymes to break down Proteins and Lipids Lipids • Acid (HCl) in the stomach Kills Bacteria • Food found in the stomach is called Chyme Small Intestine • Small intestines are roughly meters long • Lining of intestine walls has finger-like projections called villi, to increase surface area • The villi are covered in microvilli which further increases surface area for absorption Crash Course Review Small Intestine • Nutrients from the food pass into the bloodstream through the small intestine walls • Absorbs: – 80% ingested water – Vitamins – Minerals – Carbohydrates – Proteins – Lipids • Secretes digestive enzymes Large Intestine • About 1.5 meters long • Accepts what small intestines don’t absorb • Rectum (short term storage which holds feces before it is expelled) • Functions Large Intestine – Bacterial digestion • Ferment carbohydrates Absorbs more water – Concentrate wastes – Accessory Organs The Glands • Not part of the path of food, but play a critical role • Include: Liver, gall bladder, and pancreas Liver • Directly affects digestion by producing bile – Bile helps digest fat • filters out toxins and waste including drugs and alcohol and poisons 13 Gall Bladder • Stores bile from the liver, releases it into the small intestine • Fatty diets can cause gallstones Pancreas • Produces digestive enzymes to digest fats, carbohydrates and proteins • Regulates blood sugar by producing insulin Web Page Reinforcement Video On a sheet of paper, write the name of each colored organ: • • • • • • • Green: Red: Pink: Brown: Purple: Green: Yellow: How’d you do? • • • • • • • Green: Esophagus Red: Stomach Pink: Small Intestine Brown: Large Intestine Purple: Liver Green: Gall Bladder Yellow: Pancreas Great Job! References and Links • Your Digestive System and How It Works – Digestive system diagram comes from this site • • • • The Real Deal on the Digestive System Pancreas: Introduction and Index Your Gross and Cool Body - Digestive System Laurentian Regional High School Data Base - you must know the Username and Password [...]... Large Intestine Purple: Liver Green: Gall Bladder Yellow: Pancreas Great Job! References and Links • Your Digestive System and How It Works – Digestive system diagram comes from this site • • • • The Real Deal on Physiology The Digestive System www.cambodiamed.com Functions of the GI Tract Motility: • Movement of of food through the GI tract • Ingestion: • Taking food into the mouth • Mastication: • Chewing the food and mixing it with saliva • Deglutition: • Swallowing the food • Peristalsis: • Rhythmic wave-like contractions that move food through GI tract www.cambodiamed.com Functions of the GI Tract (continued) • Secretion: • Includes both exocrine and endocrine secretions • Exocrine: • HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin, elastase, and histamine are secreted into the lumen of the GI tract • Endocrine: • Stomach and small intestine secrete hormones to help regulate the GI system • Gastrin, secretin, CCK, GIP, GLP-1, guanylin, VIP, and somatostatin www.cambodiamed.com Functions of the GI Tract (continued) • Digestion: • Breakdown of food particles into subunits (chemical structure change) • Absorption: • Process of the passage of digestion (chemical subunits) into the blood or lymph • Storage and elimination: • Temporary storage and elimination of indigestible food www.cambodiamed.com Digestive System (GI) • GI tract divided into: Insert fig 18.2 • Alimentary canal • Accessory digestive organs • GI tract is 30 ft long and extends from mouth to anus www.cambodiamed.com Layers of GI Tract • Composed of tunics: • Mucosa • Submucosa Muscularis Serosa www.cambodiamed.com Mucosa • Lines the lumen of GI tract • Consists of simple columnar epithelium • Lamina propria: • Thin layer of connective tissue containing lymph nodules • Muscularis mucosae: • Thin layer of smooth muscle responsible for the folds • Folds increase surface area for absorption • Goblet cells: • Secrete mucus www.cambodiamed.com Submucosa • Thick, highly vascular layer of connective tissue • Absorbed molecules enter the blood and lymphatic vessels • Submucosal plexus (Meissner’s plexus): • Provide autonomic nerve supply to the muscularis mucosae www.cambodiamed.com Muscularis • Responsible for segmental contractions and peristaltic movement through the GI tract • Inner circular layer of smooth muscle • Outer longitudinal layer of smooth muscle • Contractions of these layers move food through the tract; pulverize and mix the food • Myenteric plexus located between the muscle layers • Major nerve supply to GI tract • Fibers and ganglia from both sympathetic and parasympathetic nervous systems www.cambodiamed.com Serosa • Binding and protective outer layer • Consists of areolar connective tissue covered with simple squamous epithelium www.cambodiamed.com Gastric Phase (continued) • Secretion of HCl is also regulated by a negative feedback effect: Insert Fig 18.30 • HCl secretion decreases if pH < 2.5 • At pH of 1.0, gastrin secretion ceases • D cells stimulate secretion of somatostatin • Paracrine regulator to inhibit secretion of gastrin www.cambodiamed.com Intestinal Phase • Inhibits gastric activity when chyme enters the small intestine • Arrival of chyme increases osmolality and distension • Activates sensory neurons of vagus and produces an inhibitory neural reflex: • Inhibits gastric motility and secretion • In the presence of fat, enterogasterone inhibits gastric motility and secretion • Hormone secretion: • Inhibit gastric activity: • Somatostatin, CCK, and GLP-1 www.cambodiamed.com Enteric Nervous System • Submucosal and myenteric plexuses contain 100 million neurons • Include preganglionic parasympathetic axons, ganglion cell bodies, postganglionic sympathetic axons; and afferent intrinsic and extrinsic sensory neurons www.cambodiamed.com Enteric Nervous System • Peristalsis: • ACh and substance P stimulate smooth muscle contraction above the bolus • NO, VIP, and ATP stimulate smooth muscle relaxation below the bolus (continued) Insert fig 18.31 www.cambodiamed.com Paracrine Regulators of the Intestine • Serotonin (5-HT): • Stimulates intrinsic afferents, which send impulses into intrinsic nervous system; and activates motor neurons • System Processes and Memory Management Objectives Upon completion of this module, you should be able to: • Identify processes on your system using the ps command • Find a process using the pgrep command • Control processes using the jobs command • Terminate unwanted processes using the kill and pkill commands Discussion – At times an application that you are running will freeze or cause your system to become inaccessible. How would you regain control of your workstation? System Process Overview Each task you perform in the Linux environment starts a process. An example of a process is using vi to edit a letter, or sending a file to the printer. Each process is assigned a unique process identification number (PID), which is used by the system to identify the process. The following pages define useful commands on how to locate a process and terminate processes. Process Hierarchy There are five types of processes on a Linux system: • Daemon • Parent • Child • Orphan • Zombie or defunct Daemon processes are processes that are started by the kernel and exist for a specific purpose. For instance, the lpd daemon exists for the sole purpose of handling print jobs. When no printing is taking place on the system, the lpd daemon is running but inactive. When a print job is submitted, this daemon becomes active until the job is finished. The login daemon provides the CDE login screen at the beginning of a user’s session and again after the user exits CDE. Following system boot-up, a process called init is invoked. This process is at the top of the process hierarchy and is responsible for spawning many system processes. The login daemon is spawned by init and init is, therefore, referred to as the parent process of the login daemon. When a user is working in a terminal window in CDE, that terminal’s PID is the parent process ID (PPID) of any commands issued in the terminal. These commands are child processes of the terminal process. The parent process receives and displays the output from the child process and then “kills” the process. If a command is issued in a terminal window and the window is closed before the command returns output, that process becomes an orphan. The system passes the orphan process to init which then becomes the parent process and terminates the child process. Occasionally a child process does not return to the parent process with its output. This process becomes “lost” in the system. The only resource this process uses is a slot in the process table; it cannot be stopped in a conventional manner. This type of process is called a zombie or defunct process. The only way to kill a defunct process is to reboot the system. Processes and PIDs Use the ps command to list the processes currently running on the system. The output of this command will display the PID number and the command associated with it. Many times a PID number is needed for use with the kill command . Command Format ps [-options] Options -e Print information about every process on the system. -f Generate a full listing. (Refer to the man pages for a description of the headings displayed.) Because of the number of processes usually running on a system, it is useful to pipe the ps -ef command to more so that the output can be read a page at a time, as in the example on the next page. Displaying a Full Listing of All Processes $ ps -ef | more UID PID PPID C STIME TTY TIME CMD root 0 0 80 16:46:41 ? 0:01 sched root 1 0 80 16:46:44 ? 0:40 /etc/init - root 2 0 27 16:46:44 ? 0:00 pageout root 3 0 80 16:46:44 ? 4:33 fsflush root 236 1 80 16:48:08 ? 0:01 /usr/lib/saf/sac root 844 1 54 12:12:10 ? 0:00 /usr/lib/lpsched aster 1292 1 80 06:48:51 console 0:01 -ksh root 241 236 69 16:48:14 ? 0:01 /usr/lib/saf/ttymon rose Digestive .. .Digestive System Regulation Digestive Phases The response to food begins even before food enters the mouth The... tandem with another hormone called cholecystokinin (CCK) Not only does CCK stimulate the 2/4 Digestive System Regulation pancreas to produce the requisite pancreatic juices, it also stimulates the... Understanding the hormonal control of the digestive system is an important area of ongoing research Scientists are exploring the role of each hormone in the digestive process and developing ways